Very low concentrations of nano-particles, or any other extremely small, gas-borne particles, are difficult to detect due to their small size and low concentrations. There is a basic need for accurate detection of nano-particles in the environment and, in particular, for detection of airborne particles that may affect human health. Detection of nano-particles and the determination of their size distribution is also a critical diagnostic tool for nano-manufacturing processes that are expected to produce close-tolerance nano-particles. Manufacturing processes that use nano-particles as a raw material may also benefit from the development of sensors capable of monitoring the size distribution of the source materials in real time. In addition to near-earth environments, large-scale nano-particle production may impact the upper atmosphere. Here, nano-particles may become electrically charged and suspended in the earth's atmosphere where unanticipated effects (such as catalysis of atmospheric chemical processes) may occur. Finally, trapping and removal of nano-particles will be very beneficial to semiconductor clean-room processes, where the presence of nano-particles is increasingly damaging.
Current detection schemes rely on laser scattering from particles that are entrained in flowing gas samples. Laser scattering techniques are not as effective for small nano-particles because the scattering cross section decreases as the sixth power of the particle radius. In addition, very clean environments have so few particles that traditional methods of particle detection may not detect particles with statistical certainty. Thus, better methods of collecting and detecting small particles are clearly desirable.